Object ids fixes

Since all associations are now using object id's instead of strings, we need to make sure all string id's get converted to mongo object ids.  Question... do we need to provide a way to override this in case strings are still needed in some scenarios?

Also making sure we pass the schema when rewriting ids.  Other wise we end up with stuff like this on the output...

"_bsontype": "ObjectID",
"id": "S7ßÑ!\u0000ès \u0000/ù"